1. Field of the Invention
The present invention relates to a flame retardant polycarbonate resin composition. More particularly, the present invention is concerned with a flame retardant polycarbonate resin composition, which comprises, in a specific ratio, an aromatic polycarbonate (A), a copolymer (B) comprising an aromatic vinyl monomer unit (b-1) and a vinyl cyanide monomer unit (b-2), a cyanide-containing, graft copolymer (C) obtained by copolymerizing an aromatic vinyl compound (c-1) and a vinyl cyanide compound (c-2) in the presence of a rubbery polymer (c-3), a (meth)acrylate-containing, graft co-polymer (D) obtained by copolymerizing an aromatic vinyl compound (d-1) and an alkyl (meth)acrylate (d-2) in the presence of a rubbery butadiene polymer (d-3), and at least one organic phosphorus compound oligomer (E). The resin composition of the present invention not only simultaneously exhibits excellent melt fluidity, impact resistance, thermal resistance and flame retardancy, but also has high stability in mechanical properties. Further, the occurrence of a mold deposit (MD) during the molding of such a resin composition is very small. By virtue of these excellent characteristics, the resin composition of the present invention has advantages for use in various industrial fields.
2. Prior Art
A resin composition comprising a polycarbonate (PC), an ABS (acrylonitrile-butadiene-styrene) resin and a phosphorus-containing flame retardant (such a resin composition is hereinafter, frequently referred to as a xe2x80x9cPC/ABS/phosphorus-containing flame retardant compositionxe2x80x9d) is a flame retardant resin composition which is free from a chlorine/iodide flame retardant. Such a flame retardant resin composition exhibits excellent mechanical properties and thermal resistance, and hence, it has been widely used as a material for housings in electric appliances and office automation machines, such as computers, printers, word processors and copying machines.
The technologies concerning the PC/ABS/phosphorus-containing flame retardant composition are described, for example, in the following patent documents: Unexamined Japanese Patent Application Laid-Open Specification No. 2-32154 (corresponding to U.S. Pat. No. 5,061,745); Unexamined Japanese Patent Application Laid-Open Specification No. 2-115262 (corresponding to U.S. Pat. No. 5,204,394); Unexamined Japanese Patent Application Laid-Open Specification Nos. 4-285655, 4-298554, 4-300937, 6-192553 and 6-228364; Unexamined Japanese Patent Application Laid-Open Specification No. 6-240127 (corresponding to W093/22382); Unexamined Japanese Patent Application Laid-Open Specification Nos. 7-11119, 7-26129, 7-33971, 7-82466, 7-145307, 7-150028, 7-196871, 7-196872, 7-196873, 7-196874, 7-331045, 7-331051, 8-3397, 8-34916, 8-34926, 8-67810 and 8-120169; Unexamined Japanese Patent Application Laid-Open Specification No. 8-127686 (corresponding to W096/07704); Unexamined Japanese Patent Application Laid-Open Specification Nos. 8-165392, 8-225737, 8-277344, 8-208972, 9-3312, 9-48912, 9-95610, 9-104811, 9-124920 and 9-143357; Unexamined Japanese Patent Application Laid-Open Specification No. 9-165518 (corresponding to EP747424); Unexamined Japanese Patent Application Laid-Open Specification Nos. 9-176471 and 9-183893; Unexamined Japanese Patent Application Laid-Open Specification No. 9-188808 (corresponding to EP771851); and Unexamined Japanese Patent Application Laid-Open Specification No. 9-194713.
In accordance with the recent tendency to reduce the weight and wall thickness of the above-mentioned types of machines, there has been a demand for a PC/ABS/phosphorus-containing flame retardant composition which simultaneously exhibits a high melt fluidity and a high impact resistance and which can therefore be advantageously used for producing light-weight and small-thickness shaped articles. However, in the above-mentioned patent documents, a PC/ABS/phosphorus-containing flame retardant composition which simultaneously exhibits satisfactorily high melt fluidity and impact resistance has not been obtained.
It has been attempted to produce a PC/ABS/phosphorus-containing flame retardant composition having a high melt fluidity by increasing the amount of ABS or SAN (styrene-acrylonitrile copolymer) contained in the resin composition. However, the obtained resin composition has a problem in that the flame retardancy of the resin composition becomes unsatisfactory so that a dripping of flaming particles is likely to occur when the resin composition is on fire. Further, such a resin composition has problems in that the impact resistance and the thermal resistance of the resin composition become low. It has also been attempted to improve the melt fluidity of a PC/ABS/phosphorus-containing flame retardant composition by using a low molecular weight polycarbonate. However, in this attempt, the impact resistance of the obtained resin composition is lowered.
Unexamined Japanese Patent Application Laid-Open Specification No. 62-25179 discloses a resin composition containing a polycarbonate, ABS and MBS (methyl methacrylate-butadiene-styrene copolymer) and U.S. Pat. No. 4,390,657 discloses a resin composition containing a polycarbonate, ABS, and an acrylic rubber-containing multi-phase composite interpolymer which is obtained by graft copolymerizing an acrylate monomer onto a butyl acrylate rubber. These patent documents describe that these resin compositions are improved in weld strength and low temperature impact resistance. However, these patent documents disclose neither a technique for improving the melt fluidity of a resin composition nor a technique for improving the flame retardancy of a resin composition. In addition, the improvement in impact resistance achieved by the use of the acrylic rubber-containing multi-phase composite interpolymer is unsatisfactory.
Unexamined Japanese Patent Application Laid-Open Specification No. 6-240127 (corresponding to WO 93/22382) and Unexamined Japanese Patent Application Laid-Open Specification No. 8-3397 disclose the use of a specialty rubber in combination with the PC/ABS/phosphorus-containing flame retardant composition in which a phosphorus compound oligomer is used as the flame retardant, wherein the specialty rubber is a complex rubber (silicone-acrylic complex rubber) obtained by a process comprising graft polymerizing a vinyl monomer onto a complex rubber comprising a polyorganosiloxane and a polyalkyl (meth)acrylate. The silicone-acrylic complex rubber used in the above-mentioned patent documents exhibits only a low reactivity with a rubber comprising a polyorganosiloxane and a polyalkyl (meth)acrylate and, accordingly, the graft polymerization of a vinyl monomer onto the above-mentioned rubber becomes difficult. Therefore, the methods disclosed in the above-mentioned patent documents are disadvantageous not only in that a complicated process is required for the production of a silicone-acrylic complex rubber, but also in that the production cost becomes high. Further, when a silicone-acrylic complex rubber is used in combination with a PC/ABS/phosphorus-containing flame retardant composition, the resultant resin composition has a disadvantage that the impact resistance is likely to be lowered during the residence of the resin composition in a molding machine for producing a molded article.
In a PC/ABS/phosphorus-containing flame retardant composition, the high thermal resistance which a PC resin inherently possesses may occasionally be lost due to the use of a phosphor-us-containing flame retardant. The thermal resistance of a resin composition is influenced by various factors, such as the properties of the flame retardant itself (e.g., thermal properties and viscosity of the flame retardant, and compatibility of the flame retardant with the resin), the ratio of the flame retardant to the resin, and the ratio of PC in the resin composition. Among these properties, the physical properties of the flame retardant used is especially important for the thermal resistance of a resin composition. Therefore, there has been a strong demand for the development of a phosphorus-containing flame retardant which does not adversely influence the thermal resistance of a PC resin.
Further, when a phosphoric ester having a low resistance to hydrolysis is used as a phosphorus-containing flame retardant for producing a PC/ABS/phosphorus-containing flame retardant composition, an ultimate molded article obtained from the resin composition suffers marked deterioration in mechanical properties. Particularly, the elongation and impact resistance of the molded article become lowered. Such a deterioration of the mechanical properties becomes significant when the molded article is placed under high temperature and high humidity conditions, and the molded article may occasionally be unable to maintain the mechanical properties which are necessary for, for example, housings of various machines. Further, it is generally difficult to reuse a material which has once undergone a marked deterioration. The above-mentioned disadvantages are likely to lead to serious problems, such as a loss of quality during a long term usage of the final product and a loss of recyclability of the final product, and therefore, there is a strong demand for techniques useful for overcoming these disadvantages.
Further, a PC/ABS/phosphorus-containing flame retardant composition prepared using a phosphorus-containing flame retardant has the following problem. When such a resin composition is subjected to molding, the phosphorus-containing flame retardant in the resin composition is likely to deposit on the surface of the mold. Such a phenomenon is called a mold deposit (MD) and the occurrence of MD is likely to lower the level of surface appearance and productivity of the molded articles. The use of a phosphoric ester oligomer-containing flame retardant tends to suppress the occurrence of MD, as compared to the use of a monophosphoric ester (such as triphenyl phosphate). However, the suppression of MD by the use of a conventional phosphoric ester oligomer-containing flame retardant is still unsatisfactory, and a further improvement has been desired.
As is apparent from the above, there has been a strong demand for a flame retardant polycarbonate resin composition which not only simultaneously exhibits excellent melt fluidity, impact resistance, thermal resistance and flame retardancy, but also has high stability in mechanical properties, and in which the amount of mold deposit generated during the molding of the resin composition is very small. However, it has conventionally been impossible to produce a flame retardant polycarbonate resin composition which exhibits all of the above-mentioned properties at a satisfactory level. The development of such an excellent flame retardant polycarbonate resin composition has therefore been desired.
In this situation, the present inventors have made extensive and intensive studies toward developing the above-mentioned excellent flame retardant polycarbonate resin composition. As a result, it has unexpectedly been found that a flame retardant polycarbonate resin composition comprising, in a specific ratio, an aromatic polycarbonate (A), a copolymer (B) comprising an aromatic vinyl monomer unit (b-1) and a vinyl cyanide monomer unit (b-2), a cyanide-containing, graft copolymer (C) obtained by copolymerizing an aromatic vinyl compound (c-1) and a vinyl cyanide compound (c-2) in the presence of a rubbery polymer (c-3), a (meth)acrylate-containing, graft copolymer (D) obtained by copolymerizing an aromatic vinyl compound (d-1) and an alkyl (meth)acrylate (d-2) in the presence of a rubbery butadiene polymer (d-3), and at least one organic phosphorus compound oligomer (E), not only simultaneously exhibits excellent flame retardancy, melt fluidity and impact resistance, but also has high stability in mechanical properties. Further, the present inventors found that the occurrence of mold deposit (MD) during the molding of such a resin composition is very small. The present invention has been completed, based on these novel findings.
Accordingly, it is a primary object of the present invention to provide a flame retardant polycarbonate resin composition which not only simultaneously exhibits excellent flame retardancy, melt fluidity, impact resistance and thermal resistance, but also has high stability in mechanical properties, and in which the occurrence of MD during the molding of the resin composition is very small.
The foregoing and other objects, features and advantages of the present invention will be apparent from the following detailed description and appended claims taken in connection with the accompanying drawings.